When should we use intern method of String on String literals

Question

According to String#intern(), intern method is supposed to return the String from the String pool if the String is found in String pool, otherwise a new string

Answer 1

As you said, that string intern() method will first find from the String pool, if it finds, then it will return the object that points to that, or will add a new String into the pool.

    String s1 = "Hello";
    String s2 = "Hello";
    String s3 = "Hello".intern();
    String s4 = new String("Hello");

    System.out.println(s1 == s2);//true
    System.out.println(s1 == s3);//true
    System.out.println(s1 == s4.intern());//true

The s1 and s2 are two objects pointing to the String pool "Hello", and using "Hello".intern() will find that s1 and s2. So "s1 == s3" returns true, as well as to the s3.intern().

Answer 2

By using heap object reference if we want to get corresponding string constant pool object reference, then we should go for intern()

String s1 = new String("Rakesh");
String s2 = s1.intern();
String s3 = "Rakesh";

System.out.println(s1 == s2); // false
System.out.println(s2 == s3); // true

Pictorial View

Step 1: Object with data 'Rakesh' get created in heap and string constant pool. Also s1 is always pointing to heap object.

Step 2: By using heap object reference s1, we are trying to get corresponding string constant pool object referenc s2, using intern()

Step 3: Intentionally creating a object with data 'Rakesh' in string constant pool, referenced by name s3

As "==" operator meant for reference comparison.

Getting false for s1==s2

Getting true for s2==s3

Hope this help!!